Central cutting region of a drilling head assembly

摘要

In one aspect of the invention, a drilling assembly comprises a head located on a rotational axis of the assembly and comprises at least one head element. At least one blade extends distally from the head. A plurality of blade degradation elements are rotationally supported on the blade. Each degradation element comprises an attack angle that affects the penetration rate of each degradation element and a laterally offset angle that primarily affects the rotational rate of each degradation element within their holders. The drilling assembly comprises a central cutting region. The blade degradation elements within the central cutting region form an attack angle of 15 to 20 degrees with the rotational axis of the drilling assembly.